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          flex布局语法
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          (adsbygoogle = window.adsbygoogle || []).push({});
      </script></div> <div class="theme-vdoing-content content__default"><h1 id="flex布局语法"><a href="#flex布局语法" class="header-anchor">#</a> flex布局语法</h1> <h2 id="一、flex-布局是什么"><a href="#一、flex-布局是什么" class="header-anchor">#</a> 一、flex 布局是什么？</h2> <p>Flex是 Flexible Box 的缩写，意为&quot;弹性布局&quot;，用来为盒状模型提供最大的灵活性。</p> <p><strong>任何一个容器</strong> 都可以指定为 Flex 布局。
</p> <div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span><span class="token punctuation">{</span>
  <span class="token property">display</span><span class="token punctuation">:</span> flex<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>行内元素</strong> 也可以使用 Flex 布局。</p> <div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span><span class="token punctuation">{</span>
  <span class="token property">display</span><span class="token punctuation">:</span> inline-flex<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>Webkit 内核的浏览器，必须加上<code>-webkit</code>前缀。</p> <div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span><span class="token punctuation">{</span>
  <span class="token property">display</span><span class="token punctuation">:</span> -webkit-flex<span class="token punctuation">;</span> <span class="token comment">/* Safari */</span>
  <span class="token property">display</span><span class="token punctuation">:</span> flex<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p><strong>注意</strong>，设为 Flex 布局以后，子元素的<code>float</code>、<code>clear</code>和<code>vertical-align</code>属性将失效。</p> <h2 id="二、基本概念"><a href="#二、基本概念" class="header-anchor">#</a> 二、基本概念</h2> <p>采用 Flex 布局的元素，称为 Flex 容器（flex container），简称&quot;容器&quot;。它的所有子元素自动成为容器成员，称为 Flex 项目（flex item），简称&quot;项目&quot;。</p> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071004.png" alt="img"></p> <p>容器默认存在两根轴：水平的主轴（或x轴）（main axis）和垂直的交叉轴（或y轴）（cross axis）。主轴的开始位置（与边框的交叉点）叫做<code>main start</code>，结束位置叫做<code>main end</code>；交叉轴的开始位置叫做<code>cross start</code>，结束位置叫做<code>cross end</code>。</p> <p>项目默认沿主轴排列。单个项目占据的主轴空间叫做<code>main size</code>，占据的交叉轴空间叫做<code>cross size</code>。</p> <h2 id="三、容器的属性"><a href="#三、容器的属性" class="header-anchor">#</a> 三、容器的属性</h2> <p>以下6个属性设置在容器上。(即设置在 display: flex; 的元素上)</p> <blockquote><ul><li><p>flex-direction      方向     决定项目的排列方向</p></li> <li><p>flex-wrap             换行</p></li> <li><p>flex-flow              方向和换行的简写</p></li> <li><p>justify-content    主轴对齐方式</p></li> <li><p>align-items          交叉轴对齐方式</p></li> <li><p>align-content      多轴线的对齐方式</p></li></ul></blockquote> <h3 id="_3-1-flex-direction属性"><a href="#_3-1-flex-direction属性" class="header-anchor">#</a> 3.1 flex-direction属性</h3> <p><code>flex-direction</code>属性决定主轴的方向（即项目的排列方向）。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">flex-direction</span><span class="token punctuation">:</span> row | row-reverse | column | column-reverse<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071005.png" alt="img"></p> <p>它可能有4个值。</p> <blockquote><ul><li><code>row</code>（默认值）：主轴为水平方向，起点在左端。</li> <li><code>row-reverse</code>：主轴为水平方向，起点在右端。</li> <li><code>column</code>：主轴为垂直方向，起点在上沿。</li> <li><code>column-reverse</code>：主轴为垂直方向，起点在下沿。</li></ul></blockquote> <h3 id="_3-2-flex-wrap属性"><a href="#_3-2-flex-wrap属性" class="header-anchor">#</a> 3.2 flex-wrap属性</h3> <p>默认情况下，项目都排在一条线（又称&quot;轴线&quot;）上。<code>flex-wrap</code>属性定义，如果一条轴线排不下，如何换行。</p> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071006.png" alt="img"></p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span><span class="token punctuation">{</span>
  <span class="token property">flex-wrap</span><span class="token punctuation">:</span> nowrap | wrap | wrap-reverse<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p>它可能取三个值。</p> <p>（1）<code>nowrap</code>（默认）：不换行。会压缩项目的宽度</p> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071007.png" alt="img"></p> <p>（2）<code>wrap</code>：换行，第一行在上方。</p> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071008.jpg" alt="img"></p> <p>（3）<code>wrap-reverse</code>：换行，第一行在下方。</p> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071009.jpg" alt="img"></p> <h3 id="_3-3-flex-flow"><a href="#_3-3-flex-flow" class="header-anchor">#</a> 3.3 flex-flow</h3> <p><code>flex-flow</code>属性是<code>flex-direction</code>属性和<code>flex-wrap</code>属性的简写形式，默认值为<code>row nowrap</code>。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">flex-flow</span><span class="token punctuation">:</span> &lt;flex-direction&gt; || &lt;flex-wrap&gt;<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <h3 id="_3-4-justify-content属性"><a href="#_3-4-justify-content属性" class="header-anchor">#</a> 3.4 justify-content属性</h3> <p><code>justify-content</code>属性定义了项目在主轴上的对齐方式。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">justify-content</span><span class="token punctuation">:</span> flex-start | flex-end | center | space-between | space-around<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071010.png" alt="img"></p> <p>它可能取5个值，具体对齐方式与轴的方向有关。下面假设主轴为从左到右。</p> <blockquote><ul><li><code>flex-start</code>（默认值）：左对齐</li> <li><code>flex-end</code>：右对齐</li> <li><code>center</code>： 居中</li> <li><code>space-between</code>：两端对齐，项目之间的间隔都相等。</li> <li><code>space-around</code>：每个项目两侧的间隔相等。所以，项目之间的间隔比项目与边框的间隔大一倍。</li></ul></blockquote> <h3 id="_3-5-align-items属性"><a href="#_3-5-align-items属性" class="header-anchor">#</a> 3.5 align-items属性</h3> <p><code>align-items</code>属性定义项目在交叉轴上如何对齐。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">align-items</span><span class="token punctuation">:</span> flex-start | flex-end | center | baseline | stretch<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071011.png" alt="img"></p> <p>它可能取5个值。具体的对齐方式与交叉轴的方向有关，下面假设交叉轴从上到下。</p> <blockquote><ul><li><code>flex-start</code>：交叉轴的起点对齐。</li> <li><code>flex-end</code>：交叉轴的终点对齐。</li> <li><code>center</code>：交叉轴的中点对齐。</li> <li><code>baseline</code>: 项目的第一行文字的基线对齐。</li> <li><code>stretch</code>（默认值）：如果项目未设置高度或设为auto，将占满整个容器的高度。</li></ul></blockquote> <h3 id="_3-6-align-content属性"><a href="#_3-6-align-content属性" class="header-anchor">#</a> 3.6 align-content属性</h3> <p><code>align-content</code>属性定义了多根轴线的对齐方式（<strong>一排项目为一根轴线</strong>）。如果项目只有一根轴线，该属性不起作用。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">align-content</span><span class="token punctuation">:</span> flex-start | flex-end | center | space-between | space-around | stretch<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071012.png" alt="img"></p> <p>该属性可能取6个值。</p> <blockquote><ul><li><code>flex-start</code>：与交叉轴的起点对齐。</li> <li><code>flex-end</code>：与交叉轴的终点对齐。</li> <li><code>center</code>：与交叉轴的中点对齐。</li> <li><code>space-between</code>：与交叉轴两端对齐，轴线之间的间隔平均分布。</li> <li><code>space-around</code>：每根轴线两侧的间隔都相等。所以，轴线之间的间隔比轴线与边框的间隔大一倍。</li> <li><code>stretch</code>（默认值）：轴线占满整个交叉轴。</li></ul></blockquote> <h2 id="四、项目的属性"><a href="#四、项目的属性" class="header-anchor">#</a> 四、项目的属性</h2> <p>以下6个属性设置在项目上。</p> <blockquote><ul><li><code>order</code></li> <li><code>flex-grow</code></li> <li><code>flex-shrink</code></li> <li><code>flex-basis</code></li> <li><code>flex</code> <code>flex-grow</code>, <code>flex-shrink</code> 和 <code>flex-basis</code>的简写</li> <li><code>align-self</code></li></ul></blockquote> <h3 id="_4-1-order属性"><a href="#_4-1-order属性" class="header-anchor">#</a> 4.1 order属性</h3> <p><code>order</code>属性定义项目的排列顺序。数值越小，排列越靠前，默认为0。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">order</span><span class="token punctuation">:</span> &lt;integer&gt;<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071013.png" alt="img"></p> <h3 id="_4-2-flex-grow属性"><a href="#_4-2-flex-grow属性" class="header-anchor">#</a> 4.2 flex-grow属性</h3> <p><code>flex-grow</code>属性定义项目的放大比例，默认为<code>0</code>，即如果存在剩余空间，也不放大。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">flex-grow</span><span class="token punctuation">:</span> &lt;number&gt;<span class="token punctuation">;</span> <span class="token comment">/* default 0 */</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071014.png" alt="img"></p> <p>如果所有项目的<code>flex-grow</code>属性都为1，则它们将等分剩余空间（如果有的话）。如果一个项目的<code>flex-grow</code>属性为2，其他项目都为1，则前者占据的剩余空间将比其他项多一倍。</p> <h3 id="_4-3-flex-shrink属性"><a href="#_4-3-flex-shrink属性" class="header-anchor">#</a> 4.3 flex-shrink属性</h3> <p><code>flex-shrink</code>属性定义了项目的缩小比例，默认为1，即如果空间不足，该项目将缩小。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">flex-shrink</span><span class="token punctuation">:</span> &lt;number&gt;<span class="token punctuation">;</span> <span class="token comment">/* default 1 */</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071015.jpg" alt="img"></p> <p>如果所有项目的<code>flex-shrink</code>属性都为1，当空间不足时，都将等比例缩小。如果一个项目的<code>flex-shrink</code>属性为0，其他项目都为1，则空间不足时，前者不缩小。</p> <p>负值对该属性无效。</p> <h3 id="_4-4-flex-basis属性"><a href="#_4-4-flex-basis属性" class="header-anchor">#</a> 4.4 flex-basis属性</h3> <p><code>flex-basis</code>属性定义了在分配多余空间之前，项目占据的主轴空间（main size）。浏览器根据这个属性，计算主轴是否有多余空间。它的默认值为<code>auto</code>，即项目的本来大小。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">flex-basis</span><span class="token punctuation">:</span> &lt;length&gt; | auto<span class="token punctuation">;</span> <span class="token comment">/* default auto */</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p>它可以设为跟<code>width</code>或<code>height</code>属性一样的值（比如350px），则项目将占据固定空间。</p> <h3 id="_4-5-flex属性"><a href="#_4-5-flex属性" class="header-anchor">#</a> 4.5 flex属性</h3> <p><code>flex</code>属性是<code>flex-grow</code>, <code>flex-shrink</code> 和 <code>flex-basis</code>的简写，默认值为<code>0 1 auto</code>。后两个属性可选。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">flex</span><span class="token punctuation">:</span> none | [ &lt;<span class="token string">'flex-grow'</span>&gt; &lt;<span class="token string">'flex-shrink'</span>&gt;? || &lt;<span class="token string">'flex-basis'</span>&gt; ]
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p>该属性有两个快捷值：<code>auto</code> (<code>1 1 auto</code>) 和 none (<code>0 0 auto</code>)。</p> <p><strong>建议优先使用这个属性，而不是单独写三个分离的属性，因为浏览器会推算相关值。</strong></p> <h3 id="_4-6-align-self属性"><a href="#_4-6-align-self属性" class="header-anchor">#</a> 4.6 align-self属性</h3> <p><code>align-self</code>属性允许单个项目有与其他项目不一样的对齐方式，可覆盖<code>align-items</code>属性。默认值为<code>auto</code>，表示继承父元素的<code>align-items</code>属性，如果没有父元素，则等同于<code>stretch</code>。</p> <blockquote><div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">.item</span> <span class="token punctuation">{</span>
  <span class="token property">align-self</span><span class="token punctuation">:</span> auto | flex-start | flex-end | center | baseline | stretch<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></blockquote> <p><img src="http://www.ruanyifeng.com/blogimg/asset/2015/bg2015071016.png" alt="img"></p> <p>该属性可能取6个值，除了auto，其他都与align-items属性完全一致。</p> <p>（完）</p> <blockquote><p>来源：</p> <p><a href="http://www.ruanyifeng.com/blog/2015/07/flex-grammar.html" target="_blank" rel="noopener noreferrer">http://www.ruanyifeng.com/blog/2015/07/flex-grammar.html<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></p> <p><a href="http://www.ruanyifeng.com/blog/2015/07/flex-examples.html" target="_blank" rel="noopener noreferrer">http://www.ruanyifeng.com/blog/2015/07/flex-examples.html<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></p></blockquote> <p>​</p></div></div> <div class="page-slot page-slot-bottom"><!-- 横向自适应 -->
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